The S⋯N noncovalent interaction: Comparison with hydrogen and halogen bonds

When one of the H atoms of SH2 is replaced by a halogen X, the S engages in a strong S⋯N interaction with the N of NH3, wherein X lies directly opposite the N. The binding energy varies from 8 kcal/mol for X = F down to 5 kcal/mol for Br. This FS⋯N geometry represents the global minimum on the HSF/NH3 potential energy surface, more stable than minima containing either a SH⋯N or NH⋯F H-bond. It is equally stable with a SH⋯N structure for X = Cl, and slightly less stable than SH⋯N for X = Br. In all cases, the S⋯N minimum is more stable than geometries containing a halogen bond.